Discoveries of microbes locked within the depths of glacial ice are opening an exciting new frontier for scientific research, while also posing an ecological predicament. As climate change causes ice masses to melt worldwide, the re-emergence of ancient bacteria and viruses threatens present day species lacking immunity to these old world pathogens.
Early this year, researcher Zhi-Ping Zhong and a team of researchers discovered 33 viral populations within two ice cores that had been extracted from the Guliya ice cap in the northwestern part of the Tibetan Plateau, in the Kunlun Mountains of northwestern China. The ice dates as far back as 15,000 years ago. All but five of the viral groups are new to science, and about half were predicted to have infected different strains of bacteria, which were also abundant in the ice.
The Tibetan Plateau is a vast, high altitude arid grassland home to species like the snow leopard, Tibetan wolf, and wild yak. It is surrounded by some of the world’s highest mountain chains including the Himalayas, the Qilian and Kunlun mountains, and the Karakoram range of northern Kashmir. Shadowed by the world’s two highest peaks, Mount Everest and K2, at an elevation that averages over 4,500 meters, the Tibetan Plateau is known to many as “the roof of the world.”
To climate scientists, however, the Tibetan Plateau and its crown of peaks is known as “The Third Pole,” since it is home to tens of thousands of glaciers containing the world’s largest non-polar reservoir of ice. These glaciers feed the most renowned Asian rivers, including the Yangtze, Yellow, Mekong, and Ganges which stretch thousands of kilometers into the arid regions of China and Pakistan and supply water to almost a third of the world’s population.
In their paper, which is currently circulating for comment in advance of peer-review, the researchers explain that the shallow plateau core was drilled in 1992 at a depth of 35 meters while the summit core was drilled in 2015 at a depth of 52 meters. The viral populations are quite dissimilar between the two ice cores and are also different at various depths, “presumably representing the very different climate conditions” at the time when the viral particles settled down into the snow to be compacted into ice.
Video from Kevin Bakker: Ice core drilling in Antarctica (circa 2009) for the purposes of studying bacterial community structure.
Though the first reports of microbes being found in glacial ice occurred in the early twentieth century, they were largely neglected until the 1980s when scientists began investigating organisms in an ice core from Vostok, in Eastern Antarctica. This discovery sparked a surge of glacier ice-core sampling at the end of the twentieth century. However, most studies focused on bacterial communities.
Kevin Bakker, an infectious disease modeler at the University of Michigan, studied bacterial community structure in Antarctic water and ice cores in 2008-09. Once his team extracted a core, it was melted down very slowly, “at the room temperature of the icebreaker we were on, so around 40-50 degrees Fahrenheit, to make sure the bacteria were kept alive,” Bakker said in an interview with GlacierHub. “Bacteria pop very easily,” he added, “and we needed them alive to see which organisms were eating the radioactive food we fed them… to see which bacteria were active in the community.”
But for viruses, the definition of whether they are living or not is a moot point, since the DNA/protein complex (while not technically living) simply takes over its host cell — which most of the time is a bacterium. Zhi-Ping Zhong’s team wrote, “information about viruses in these habitats is still scarce, mainly due to the low biomass of viruses in glacier ice and the lack of a single and universally shared gene for viruses,” which can be used for genome sequencing.
In fact, the authors wrote, “there are only two reports of viruses in glacier ice.” They include the Vostok study, as well as a study that found “tomato-mosaic-tobamovirus RNA in a 140,000-year old Greenland ice core.” Viral genomes from glacier ice have not been previously reported, and “their impacts on ice microbiomes have been unexplored.”
Moreover, prior to this study, no specific decontamination method existed. In an interview with Vice, Scott O. Rogers, a professor at Bowling Green State University, said “the biomass is so low that anything you contaminate it with on the outside is going to be at much higher concentrations than anything on the inside of the ice core.” Because it is easy to contaminate ancient microbes with modern ones, the researchers developed a new “ultra-clean” method for isolating pure samples from the ice cores.
The ice cores had been sealed in plastic tubing, covered with aluminum, and transferred at -20 degrees Celsius from the drilling sites to freezers in Lhasa, Beijing, Chicago, and finally to Byrd Polar and Climate Research Center at Ohio State University. In a sub-freezing temperature controlled room, researchers began extracting their samples by first shaving off half a centimeter from the outer contaminated layer of ice. The cores were then washed with ethanol to dissolve another layer, and finally sterile water was used to wash the final half centimeter away.
The pristine inner ice was then methodically melted down and filtered, and steps were taken to identify the virus after extracting the microbial DNA. The virus’s age could be determined by counting the ice layers, just as you would count rings in a tree. To be even more precise, the researchers also dated carbon and oxygen isotopes found in each ice layer.
Ancient microbes provide researchers a window into Earth’s evolutionary and climatic past. “We are very far from sampling the entire diversity of viruses on Earth,” Chantal Abergel, an environmental virology researcher at the French National Centre for Scientific Research, told Vice. Unfortunately, glaciers around the world are shrinking at an alarming rate. The Tibetan Plateau itself has lost a quarter of its ice since 1970, so the race is on to collect as much knowledge as possible with what’s left.
Despite its extreme altitude, the glaciers on the Tibetan Plateau are latitudinally situated to receive a great deal of sunlight, and like the other two, this third pole is warming faster than the global average. In the IPCC special report on the cryosphere, scientists warn that two thirds of its remaining glaciers are bound to disappear by 2100. “This will release glacial microbes and viruses that have been trapped and preserved for tens to hundreds of thousands of years,” wrote Zhi-Ping Zhong’s team.
“At a minimum, this could lead to the loss of microbial and viral archives that could be diagnostic and informative of past Earth climate regimes,” the researchers added. However, “in a worst-case scenario, this ice melt could release pathogens into the environment.”
This possibility is very real. Bakker pointed out that in 2016, the anthrax virus escaped from a frozen reindeer carcass, killing a 12-year old boy and hospitalizing about twenty others, when permafrost melted in the Siberian tundra. Frozen microbes released through ice melt are still able to reinfect their targets, but while “there are a ton of viruses, only a few actually infect humans,” Bakker explained. Most ancient viruses pose more of a risk to bacteria. Still, it is important not to underestimate the “dangers encased in ice,” Rogers warned in his interview with Vice.
Zhi-Ping Zhong’s study represents a major advance in the field of virology. It shows how frozen creatures can inform predictions about the types of microbes that may re-emerge with climate warming, and what this could potentially mean for the future of our biosphere.
Video from Kevin Bakker: Bakker’s research team encounters some friends on their scientific expedition in Antarctica in 2009. Perks of being a scientist!
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